Ordnance survey maps are maps that show altitude in relation to a 'known' ordnance datum. An ordnance datum is a point of particular altitude. In the UK, that ordnance datum for ordnance survey maps is the mean sea level at Newlyn in Cornwall. Ordnance survey maps typically show topography, by means of contour lines and spot heights. General land detail, such as grass-land, forest, marsh. In addition roadways, railways, footpaths and bridleways are shown. This makes ordnance survey maps of particular use for anyone wishing to navigate on foot. And this remains one of the most popular uses for this type of map. Ordnance survey maps are maps that show altitude in relation to a 'known' ordnance datum. An ordnance datum is a point of particular altitude. In the UK, that ordnance datum for ordnance survey maps is the mean sea level at Newlyn in Cornwall. Ordnance survey maps typically show topography, by means of contour lines and spot heights. General land detail, such as grass-land, forest, marsh. In addition roadways, railways, footpaths and bridleways are shown. This makes ordnance survey maps of particular use for anyone wishing to navigate on foot. And this remains one of the most popular uses for this type of map.
Datum and gps
The name dates back to World War II. Much of the mapping carried out during the war was done by the Department of Ordnance (the guys who take care of munitions, artillery, tanks etc.). Their maps then, were known as Ordnance Survey maps. Today, Ordnance Survey maps are carried out by civilian teams and have nothing to do with ordnance but the name has stuck.
A reconnaissance involving the investigation, detection, location, marking, initial identification and reporting of suspected unexploded explosive ordnance, by explosive ordnance reconnaissance agents, in order to determine further action.
Perhaps you mean MLLW? If so, it is the Mean Lower Low Water; a reference point for all other measurements of Datum.
An Ordnance Survey Bench Mark is a surveying mark made by the Ordnance Survey to record heights above Ordnance Datum. They are typically found on buildings, bridges, or other structures and are used as reference points for altitude measurements.
above ordnance datum!
Above Ordnance Datum is a reference elevation used in surveying that is based on the mean sea level. It provides a standard benchmark for measuring height or altitude across different locations. This datum is commonly used in the UK and other countries for mapping and surveying purposes.
Sea level rises and falls, so a datum line was put by the British Ordnance Survey on a harbour wall at Newlyn, Cornwall. It is from this datum line that mean sea level is measured.
The highest motorway in the UK is the M62 near the boundry between Yorkshire and Lancashire which reaches 372 metres (above ordnance datum)at it's peak. == ==
Take a look at this Ordanance Survey page. http://benchmarks.ordnancesurvey.co.uk/pls/htmldb/f?p=111:7:6255072357299077241::NO:7:: Type in a kilometer square grid in the form "SP9013" for instance. This page will give you a conversion factor. It seems a little ambiguous as to whether the figure they give you is to convert Newlyn to Liverpool or vica versa. I am still investigating.
Ordnance survey maps are maps that show altitude in relation to a 'known' ordnance datum. An ordnance datum is a point of particular altitude. In the UK, that ordnance datum for ordnance survey maps is the mean sea level at Newlyn in Cornwall. Ordnance survey maps typically show topography, by means of contour lines and spot heights. General land detail, such as grass-land, forest, marsh. In addition roadways, railways, footpaths and bridleways are shown. This makes ordnance survey maps of particular use for anyone wishing to navigate on foot. And this remains one of the most popular uses for this type of map. Ordnance survey maps are maps that show altitude in relation to a 'known' ordnance datum. An ordnance datum is a point of particular altitude. In the UK, that ordnance datum for ordnance survey maps is the mean sea level at Newlyn in Cornwall. Ordnance survey maps typically show topography, by means of contour lines and spot heights. General land detail, such as grass-land, forest, marsh. In addition roadways, railways, footpaths and bridleways are shown. This makes ordnance survey maps of particular use for anyone wishing to navigate on foot. And this remains one of the most popular uses for this type of map.
Datum is not the plural of data. Datum is singular, and its plural form is data.
Datum and gps
Correction: What is hydrographic datum? not "hydrography"
A datum in land surveying is a known point or elevation used as a reference when measuring and mapping the land. It serves as the basis for establishing the positions of other points, helping to ensure accuracy and consistency in surveying work. Common datums include the North American Datum (NAD) and the World Geodetic System (WGS).
The North American Datum of 1927 (NAD 27) is "Thehorizontal control datum for the United States that (was) defined by (a) location and azimuth on the Clarke spheroid of 1866, with origin at (the survey station) Meades Ranch." ... The geoidal height at Meades Ranch (was) assumed to be zero. "Geodetic positions on the North American Datum of 1927 were derived from the (coordinates of and an azimuth at Meades Ranch) through a readjustment of the triangulation of the entire network in which Laplace azimuths were introduced, and the Bowie method was used." (Geodetic Glossary, pp. 57)